Activated carbons with and without surface functional groups were prepared by heat treatment, and their performance in adsorptive removal of 4,6-dimethyldibenzothiophene, a known refractory sulfur compound in nhexane solvent, at normal temperature and pressure was examined. The results showed that the surface functional groups increased the adsorption capacity of 4,6-dimethyldibenzothiophene, implying the presence of C-O complex sites introduced by oxidation, in addition to C pi sites, which adsorb aromatic compounds through pi-pi interactions. The adsorption affinity for 4,6-dimethyldibenzothiophene calculated by the Bi-Langmuir equation was 2.5 times higher for C-O complex sites than C pi sites. The effects of non-polar and polar solvents on the adsorption of 4,6-dimethyldibenzothiophene were also compared. In non-polar solvent, activated carbons with surface functional groups showed increased adsorption capacity, while in polar solvent they showed the opposite tendency. Moreover, the influence of 1-methylnaphthalene as a competitive inhibitor in n-hexane solvent was examined at a constant concentration of 4,6-dimethyldibenzothiophene. The increase in 1-methylnaphthalene concentration caused a decrease in the adsorption capacity of 4,6-dimethyldibenzothiophene on C pi sites but did not affect the adsorption on C-O complex sites. Therefore, it was concluded that the C-O complex sites are effective for the adsorption of polar compounds. Furthermore, the introduction of acidic functional groups or other sites that selectively adsorb sulfur compounds could be effective for the adsorptive removal of sulfur compounds such as 4,6-dimethyldibenzothiophene in fuel oil.